This invention relates to an improved therapeutic unloading apparatus and method.
Both manual and automatically driven therapeutic devices have been known in the art for quite some time. For example, physical therapists have for years treated patients with lower extremity problems in sitting positions. Whether the therapy is manual or mechanical, there is mounting evidence that rehabilitating individuals in this sitting position is less than optimal because the training does not carry over well into an upright position. Because humans function largely on their feet, the inadequacy of prior art therapy in the sitting position is a serious problem. The problem with prior art non-upright therapy lies in the forces that are generated in the upright position on an individual with a lower extremity or back injury. This is precisely why therapy in the lying or sitting position has been used in the past.
Some therapeutic devices attempt to enable therapy while in an upright position. An example of an upright therapeutic device is disclosed in Jones U.S. Pat. No. 4,973,044 which can provide a lifting force on patients while they are either walking or performing motor activities that involve relatively low speed, low frequency vertical motions (i.e. sitting down or getting out of bed). A complicated, space-gobbling device, it also forces the user to follow a circular path. The circular path of this and other devices may be suitable for a slow walk, but is detrimental to a patient's recovery when running because it altars the normal stride substantially.
Another example of a lifting device for patients is Futakami U.S. Pat. No. 4,907,571. Once again, it is designed to be utilized with a patient that is walking or performing motor activities that involve relatively low speed, low frequency vertical motions.
A drawback to the lifting devices known in the art is that if the devices described in the prior art are subjected to rapid or oscillating vertical motions, such as a patient would generate while walking at speeds of 4 to 5 mph, running, jumping, or squatting, the response time of the known pneumatic air cylinders, pulleys and counterweights, or hydraulic cylinders is insufficient to maintain a uniform lifting force on the patient. Simply put, the mechanical natural frequency of the prior art systems is too low and results in significant oscillations in lifting force, if the device is used at other than relatively low speeds, which tend toward being out-of-phase with the vertical oscillation of the patient as the frequency of the vertical oscillation is increased. This results in a very uncomfortable and possibly harmful jerking of the patient during activities where higher frequency vertical motions are required, again, such as fast walking, running or jumping. Thus, there is need in the art for providing a therapeutic unloading apparatus and method which allows much higher system natural frequencies, produced while doing anything other than a slow walk, and which provides a uniform lifting force over a wide range of vertical travel and through higher oscillatory frequencies of that vertical travel. It, therefore, is an object of this invention to provide an improved therapeutic unloading apparatus and method for automatically maintaining a set load while the load varies, back and forth, from more than to less than the set load.